What happened
On May 3, 1975, during the East Swiss Glider Championships, a De Havilland Chipmunk Mk 22, registration HB-TUI, was performing glider towing operations at the Schaffhausen airfield. Following the fourth towing mission of the day, the pilot returned to the airfield, unhooking the glider at an altitude of approximately 30 meters.
While executing a tight right-hand turn into the downwind leg for runway 25, the aircraft was flying at an altitude between 50 and 70 meters. As the pilot initiated a landing turn with a significant bank angle of approximately 50 degrees, the aircraft lost airspeed and entered a spin. The aircraft struck the ground approximately 700 meters northeast of the runway threshold at 12:41 local time. The impact resulted in the death of the pilot and the total destruction of the aircraft, though minimal damage was caused to the surrounding land.
The investigation
The investigation, conducted in collaboration with the Schaffhausen Cantonal Police, examined the aircraft wreckage, weather conditions, and pilot records. Technical analysis of the HB-TUI revealed that the flaps were fully extended and the center of gravity was within permissible limits. No pre-existing mechanical defects were found in the flight controls or engine components.
Meteorological data indicated overcast skies with visibility of approximately 10 km. Notably, the area was experiencing strong, gusty winds from the west, shifting toward the northwest, with gusts potentially reaching 10 to 20 knots. The investigation also reviewed the pilot's extensive flying experience and confirmed there were no evidence of medical impairment or intoxication at the time of the accident.
Findings
- The aircraft fell below the minimum flying speed while executing a landing turn with a high bank angle.
- This loss of airspeed triggered a spin, which could not be recovered due to the low altitude of 50–60 meters.
- The presence of gusty winds likely made maintaining a stable airspeed more difficult and should have prompted the pilot to fly at a higher safety margin.
- The pilot's flight tactics were deemed inappropriate, possibly due to an attempt to maintain the same pattern size as slower aircraft operating in the area.